The present invention relates to a method and apparatus for automatically controlling welding, in particular, a method and apparatus for automatically controlling welding by monitoring the wire interaction position.
Welding is widely used in many manufacturing processes in order to join components together. If the particular welding process is carried out repeatedly then it may be carried out by a robot as opposed to by an operator. This provides a number of benefits including improved repeatability. However, it is still necessary for an operator to monitor the welding process.
An operator continually visually assesses the weld deposition through monitoring a visual display unit (VDU) which is attached to a camera that is focussed on the weld point arc. Using a hand-held teach pendant that is connected to the robot, the operator can control the robot, the wire feed and the welding parameters. When the operator visually determines from the VDU that the weld deposition is not ideal, the wire feed and the welding parameters are manually overridden using the teach pendant.
For example, if the wire makes contact with the component during the welding deposition process, the integrity of the weld will be compromised at these locations. This is because the wire will not become fully molten at these locations and there is the possibility of partial wire fusion, which will affect the surface roughness of the weld deposition and the uniformity of deposition build-up. This is known as the “stubbing” effect. Further, if left unchecked, partial wire fusion can lead to the wire leaving the weld arc and solidifying on the substrate or on a previous deposited layer. This may result in activation of a robot collision control system as the robot tries to continue along a pre-programmed path. This will cause a process emergency shutdown. Therefore, when a skilled operator notices that stubbing may be about to occur, a parameter, such as the wire feed rate, is altered using the teach pendant to avoid it.
In another example, if the wire is fed in too slowly then the integrity of the deposition will be compromised at these locations. The semi-plastic relationship between the wire and the weld pool becomes intermittent and will break. This will cause an intermittent balling effect on the end of the wire, which will ultimately fall off leading to an interrupted supply of material and inconsistent weld deposition. This “blobbing” effect is known as burnback. The aforementioned effect will have an effect on subsequent deposition layers unless it is rectified by adding additional wire at those specific locations. Therefore, when a skilled operator notices that burnback may be about to occur, a parameter, such as the wire feed rate, is altered using the teach pendant to avoid it.
Whilst the manual intervention of the operator is satisfactory, it is not ideal and has a number of drawbacks. The process relies heavily on operator judgement and skill which will vary between operators. This means that the quality of the welding process may differ depending on who is operating the machine. The manual intervention also relies on the reaction time of the operator and on the system reaction time. This can result in a delay in appropriate action being taken. It also may not be possible for the operator to look at the VDU for long periods of time. This can result in the welding process having to be periodically suspended. Further, the process is reliant on the attention span of the operator which again may vary between operators.
It is therefore desirable to provide an automatic welding method and apparatus which reduces the reliance on an operator.